It has heretofore been proposed in U.S. Pat. No. 1,650,612 to Deniston of Nov. 29, 1927 to rotate a stack of discs relative to a coaxial stack of fixed discs on a horizontal axis within a casing to generate frictional heat in hot water flowing through the lower portion of the casing. In this heating device a supply of oil is contained in the upper portion of the casing to lubricate the discs and to float on the water at a predetermined level.
In U.S. Pat. No. 3,333,771 to Graham of Aug. 1, 1967, a pair of vaned rotors are each enclosed within a chamber of a casing, and mounted to rotate in a vertical plane on a horizontal axis as depicted in FIG. 7 thereof. As in the Deniston patent water flows through the device and is heated by friction.
In U.S. Pat. No. 4,004,553 to Stenstrom of Jan. 25, 1977 a single disc like rotor is revolved on a horizontal axis in a vertical plane, within a casing to heat water passing through the device.